The present invention relates to a system and method for rapid weighing and metering of items. More particularly it relates to postage metering systems used to weigh, determine postage for, and meter (i.e. imprint with a postal indicium representative of the postage determined) mail pieces or the like.
Postal scale systems are well known. Such scale systems weigh a mail piece and determine the appropriate postage for that mail piece as a function of the weight. Postal mailing systems where a mail piece is transported onto a postage scale system, the appropriate postage is determined, and the mail piece is then transported to postage metering system for imprinting with a postal indicium representative of the postage determined are also known. One such system is described in U.S. Pat. No. 4,742,878; issued May 10, 1988. In such systems there is a constant need to increase the rate at which the scale can determine the weight of a mail piece in order that the throughput of the system can be increased. U.S. Pat. No. 4,787,048; issued: Nov. 22, 1988, discloses one approach to decreasing the time required for a postage scale system to determine the weight of a mail piece. The system disclosed in this patent takes advantage of the structure of postage rate charts, i.e., the function that relates the weight of the mail piece to the appropriate postage amount. Such rate chart provides a constant postage value for all weights in a weight range between a pair of predetermined weight breaks. The system of the ""048 patent takes advantage of this by use of an method where a first estimate of the weight is made and used to determine the postage amount unless the first estimate is within a predetermined distance of a break point, in which case a second more accurate estimate is made.
A basic cause of the delay in determining weight for a mail piece is the tendency for a scale system to oscillate in response to the arrival of the mailpiece on the system. These oscillations are damped, but only slowly arrive at a new stable output value representative of the weight of the mail piece. Heretofore systems have relied on an averaging process over a number of samples taken over a number of cycles of the oscillations to approximate the weight output. While systems using such averaging type methods have generally proved satisfactory in the past, further decreases in the time required to determine a weight are still sought. Thus it is the object of the present invention to provide a scale system, and a postage metering system incorporating such scale system, which can more rapidly determine the weight of a mailpiece or the like.
The above object is achieved and the disadvantages of the prior art are overcome in accordance with the present invention by means of a system for determining a weight for an item, including: a scale system for generating a digital output signal, and a data processing system. The scale system includes: a support for supporting said item; and a transducer for generating said digital output signal, said signal being representative of an instantaneous response of said support. In response to said digital output signal the data processing system: detects the presence of said item on said support; then stores a sequence of values of said digital output signal, said sequence initially consisting of a first predetermined number of initial values of said digital output signal; determines a difference, D, between a maximum value in said sequence and a minimum value in said sequence; determines an average, A, of a second predetermined number of latest values in said sequence; determines if an absolute value of (Bxe2x88x92A) is less than D, where B is a weight break between weight ranges; and, if so updates said sequence by replacing a third predetermined number of earliest values in said sequence with said third predetermined number of new latest values of said digital output signal; and returning to redetermine D and continue; and, if not calls said weight as said average A.
In accordance with one aspect of the present invention the first predetermined number is selected so that said initial values cover a time period of approximately 60 milliseconds.
In accordance with another aspect of the present invention the second predetermined number is selected so that said latest values cover a time period of approximately 40 milliseconds.
In accordance with another aspect of the present invention the third predetermined number is selected so that said earliest values and said new latest values cover time periods of approximately 2 milliseconds.
In accordance with another aspect of the present invention the digital output signal has a sampling interval less than or equal to approximately 2 milliseconds.
In accordance with another aspect of the present invention 0 weight is not a weight break; so that, for a first weight range, potential errors greater than xc2xd said first weight range can be accepted.